eljobso - 7 months ago 26

Python Question

I have two lists, which contains list elements, e.g:

`list1 = [['placeholder1', {'data': 'data1'}], ['placeholder2', {'data': 'data2'}], ['placeholder2', {'data': 'data1'}]]`

list2 = [['placeholder2', {'data': 'data2'}], ['placeholder3', {'data': 'data5'}]]

intersection_result = [['placeholder2', {'data': 'data2'}]]

The structure of the sub-list elements is just an example. It can also happen that all the sub-list elements contains strings

`['asdf', 'qwert']`

`['sdfs', 232]`

How can I get the intersection of lists elements which are identical in both lists?

Answer

If my understanding is correct, you can get the intersection by checking and selecting `any()`

of the elements in the smallest list which are equal to ones in the larger one.

With a comprehension, this would look like this:

```
intersection_res = [l for l in min(list2, list1, key=len) if any(l == l2 for l2 in max(list1, list2, key=len))]
```

This uses, `min`

and `max`

with a key assigned to `len`

to always select from the smaller list and check against the larger one.

This yields:

```
print(intersection_res)
[['placeholder2', {'data': 'data2'}]]
```

This comprehension can be trimmed down if you pre-assign the min-max lists or, of course, if you are always certain which list is larger than the other:

```
sm, la = list1, list2 if len(list1) < len(list2) else list2, list1
intersection_res = [l for l in sm if any(l == l2 for l2 in la)]
```